The trackpad on your MacBook is a very delicate and should be treated with extreme care when cleaning. Apple strongly warns against using any type of cleaning solution on the trackpad [source: Apple.com]. This includes window cleaner, alcohol and ammonia. Instead, simply use water on a barely damp, lint-free soft cloth and wipe off any excess moisture with a clean, dry cloth of the same material.
If your white MacBook trackpad has become discolored, there may be a solution. Although Apple does not actually suggest the technique on its support site, some techies recommend using a Mr. Clean Magic eraser to gently rub away the grit and return it to its original white luster.